MUMBAI -- The Mumbai police on Monday hunted for Vidyasagar Rajbhar, who they identified as the "main accused" in the double murder of installation artist Hema Upadhyay and her lawyer, two days after their bodies were found in a drain packed in cardboard boxes.

The investigators zeroed in on Vidyasagar as the main culprit following sustained questioning of the four persons detained in connection with the murders of Hema Upadhyay (43) and her lawyer Harish Bhambhani (65).

"The questioning of the four detainees, including the one held in Varanasi, led to the information that the murder took place at the behest of a person called Vidyasagar Rajbhar," a senior police officer, who is part of the probe team, said.

Police have now launched a manhunt for Vidyasagar, who is a resident of Shamsi Housing Society in suburban Kandivali (West), he said.

On Saturday night, the day they were believed to have been killed, it was Vidyasagar who had called Hema on her mobile at 7.30 pm, the officer said.

Vidyasagar's arrest will help the police join the missing dots, he added.

Shivkumar Rajbhar alias Sadhu, who was on Monday detained by the Uttar Pradesh Special Task Force in Varanasi following a request by the Mumbai police, went public with the claim that the two were killed under instructions from Vidyasagar.

"We killed them under orders of Vidya," he told a TV channel while seated in a police vehicle upon his detention. Asked how the killings were executed, he said, "We used handkerchiefs soaked in a chemical."